MEMS acoustic transducers for application in portable communication devices such as mobile terminals and hearing prostheses must be robust devices of small size and low cost and still maintain good electro-acoustic performance, reliability and operability. A significant issue in keeping the manufacturing costs low and reliability high for MEMS acoustic transducers is to reduce the number of separate components that need to be manufactured, tested and assembled. The assembly of multi-component MEMS acoustic transducers has several drawbacks due to the small dimensions of each of these components and the required precise alignment of each of these components. The delicate assembly process increases manufacturing time and leads to yield loss, which translates to increased manufacturing costs.
EP 0 561 566 B1 discloses a silicon microphone assembly, which comprises at least two separate components: a MEMS transducer die and a base member. The MEMS transducer die comprises an integrally formed diaphragm and back plate structure, a FET circuit and voltage bias source. A through going aperture extends from an upper portion of the MEMS transducer die, where the diaphragm and back plate structure is arranged, from beneath the back plate to a lower surface portion of the MEMS transducer die. The base member is secured to the lower surface of the MEMS transducer die by a wafer-level bonding process so as to seal the through going aperture at the lower surface portion of the MEMS transducer die and create a closed back chamber for the silicon microphone assembly. The prior art reference does not disclose how and where electrical terminals or bumps are located on the described silicon microphone assembly to provide connectivity to an external carrier such as a PCB.
US 2005/0018864 discloses a silicon microphone assembly which comprises three separate components: a MEMS transducer die, an integrated circuit die and a conventional PCB based substrate. The MEMS transducer die and the integrated circuit are attached to an upper surface of the PCB based substrate and interconnected with electrical traces. Plated feed-trough holes between the upper and lower opposing surface establish electrical connections to the lower surface of the PCB based substrate which also holds electrical terminals or bumps for electrically connecting the silicon microphone assembly to an external PCB. The lower surface is substantially plane and the electrical bumps are positioned to allow attachment of the silicon microphone assembly to the external PCB by conventional reflow soldering processes. Respective electrical contact pads of the MEMS transducer die and the integrated circuit substrate or die are wire-bonded to corresponding pads arranged on the upper surface of the PCB based substrate. An indentation or aperture in the PCB substrate arranged below the diaphragm and backplate structure of the MEMS transducer die serves as a back chamber or volume for the MEMS transducer die. An electrically conductive lid or cover is attached around the periphery of the upper portion of the PCB substrate to shield the MEMS transducer die and the integrated circuit from the external environment such as from light and moisture etc. A grid is placed in the sound inlet port formed in the electrically conductive lid and the inner volume, enclosed below the electrically conductive lid and the upper surface of the PCB substrate, makes up the front chamber of the silicon microphone assembly.
U.S. Pat. No. 6,522,762 discloses a silicon microphone assembly formed in a so-called “chip-scale package”. The silicon microphone assembly comprises a MEMS transducer die, a separate integrated circuit die and a silicon carrier substrate with through holes formed therein. The MEMS transducer die and the integrated circuit are adjacently positioned and both attached to an upper surface of the silicon carrier substrate by flip chip bonding through respective sets of bond pads. The MEMS transducer die and the integrated circuit are interconnected with electrical traces running on the silicon carrier substrate. Feed-through structures between upper and lower opposing surfaces of the silicon carrier substrate establish electrical connections to the lower surface of the silicon substrate which also holds electrical terminals or bumps for electrically connecting the silicon microphone assembly to an external PCB. The lower surface is substantially plane and the electrical bumps are positioned to allow attachment of the silicon microphone assembly to the external PCB by conventional reflow soldering processes.
Akustica Inc. has announced, in Electronic Design Magazine on Jun. 9, 2003, an analog CMOS IC which comprises an array of 64 micromachined condenser microphones etched in silicon and integrated with an MOSFET amplifier.
U.S. Pat. No. 6,829,131 describes a MEMS die with an integral digital PWM amplifier connected to a silicon membrane structure adapted to generate a sound pressure signal by electrostatic actuation.
It is an object of the present invention to provide an improved MEMS acoustic transducer, which is formed on a single semiconductor die, whereby wafer-level bonding processes and/or the assembly of several components can be avoided in order to produce the MEMS acoustic transducer.